The present invention relates to an appartus for sensing the presence of objects within a selected region of space. In particular the present invention relates to object sensing devices which are useful in connection with the operation of automatic doors or other automatically moving equipment.
In accordance with the prior art, it has been known to make use of light or radiation emitting equipment and radiation detecting equipment for the purpose of sensing the presence of an object or person in a particular region of space. One application for such object sensing equipment is in connection with the operation of an automatically operated door. In this case it is desirable to arrange the equipment to sense the approach of a person or an object, such as a shopping cart, from one direction of the door in order to activate the door to move it to the open position. It is likewise desirable to sense the presence of an object or person on the opposite side of the door to prevent the door from striking the person during the opening operation. Another sensing function is to determine when the person has passed through the doorway, and clear of the swing of the door, to enable closing of the door after the person has entered through the doorway.
The most reliable prior-art method for sensing the presence of a person is to provide pressure sensitive doormats which provide a signal in response to the weight of a person standing thereon. Such doormats must be provided on both sides of the door. On the approach side the doormat senses the presence of a person who wishes to pass through the doorway. On the inside of the door, in the area which includes the swing path of the door, the mat is provided to sense the presence of a person or object in the path of the door and provides a signal which prevents the door from opening and causing injury to the person or damage to the object thereon. The inside swing path doormat is also used to prevent closing of the door during the time when a person is passing through the doorway. After there is no weight on either of the doormats, the door is permitted to close.
The use of pressure sensitive doormats in connection with the operation of a swinging door in accordance with the prior art, while being the most reliable known method for detecting the presence of a person or object, has a disadvantage, which is normally associated with the use of a doormat installation on a high traffic floor. The doormats used to sense the presence of a person or object are subject to wear from the passage of traffic thereover. In addition, the doormats are usually in an outdoor entry location where they will be subjected to rainwater and to damage from ice, snow, and possibly salt or other corrosive chemicals used to clear ice and snow.
A further problem with the doormat sensing devices is the fact that it becomes difficult to tell when the device has failed. Failure of the swing path doormat can result in injury to a person and consequent liability to the owner or occupant of the premises in which the door has been installed.
There have also been provided object sensing devices wherein a radiation source is provided which sends radiation along a selected path toward a radiation sensing element. When an object or person enters the path of the radiation, the absence of the radiation being received at the sensing element provides an indication that there is an object or person in the path of the beam. The use of the beam-path type sensor provides a certain "fail safe" reliability because of the fact that a beam must pass completely through the path in order to be detected and provide an indication of a safe condition. It becomes necessary, however, in connection with the operation of a swinging door, to provide a great many emitters and detectors to provide adequate assurance that a small child is not within the path of the swinging door.
U.S. Pat. No. 3,852,592 to Scoville describes a prior art door opening control apparatus which includes an emitter mounted above the doorway which sends infrared radiation along a downwardly directed energy beam which spans a path of travel of pedestrian traffic approaching the doorway. There is provided a sensing element which is mounted on the jam of the doorway and which has a receiving beam pattern of sensitivity which is generally horizontally disposed, so that there is provided an intersection of the infrared radiation beam from the emitter and the horizontal sensing beam pattern from the receiver, which defines a protected area in space. The patent states that additional emitters may be provided, as requried, to provide additional protection in additional regions in space.
While the apparatus described by Scoville may be effective in ordinary circumstances for detecting objects which are in the region defined by the intersection of the two beams, problems may arise from the fact that the door swings into the region of intersection of the two beams, and the door may interfere with operation of the system. In addition, the system may be sensitive to its installation, since the emitter and the detector are located at different locations, and the operation of these devices is sensitive to their locations and to their environment. Further, the system may fail to detect small objects, for example an infant crawling below the horizontal beam.
It is therefore an object of the present invention to provide a new and improved object detecting apparatus.
It is a further object of the present invention to provide such an apparatus which has a single location for emitters and detectors.
It is a further object of the present invention to provide such an apparatus which is less sensitive to the environment of its installation, and is less sensitive to changes in the reflectivity of the object to be detected.